This invention relates to laser sensors using heterodyned laser light.
In recent years, lasers have been put to use in molecular diagnostics. Robert Frankel et al. U.S. Pat. No. 5,637,458 (the disclosure of which is incorporated herein by reference) describes a system for biomolecular separation and detection of a molecular species that uses a solid state laser detector formed with a sample channel. The presence of a molecular species is indicated by a frequency shift in the laser""s output which is detected by optical heterodyning the laser""s output with the output of a reference laser. The interior of the sample channel can, optionally, be coated with a ligand for binding a molecular species of interest. The system involves rather complex preprocessing of the sample by electro-osmotic separation in channels that are lithographically formed in a two dimensional planar substrate and/or by a nanostructural molecular sieve formed of spaced apart posts defining narrow channels. Although an at tempt at integrated system is provided by U.S. Pat. No. 5,637,458, it does not entirely provide a fully integrated optical chip device.
Also recently, highly coherent semiconductor lasers and laser arrays have been developed primarily for telecommunications applications. See for example C. E. Zah et al., IEEE Photon. Technol. Lett., vol. 8, pp 864-866, July, 1996. In addition, widely tunable semiconductor lasers have been developed, in particular, sampled-grating distributed Bagg reflector (SGDBR) lasers. See, for example xe2x80x9cTunable Sampled-Grading DBR Lasers with Integrated Wavelength Monitors,xe2x80x9d by B. Mason et al., IEEE Photonics Technology Letters, Vol. 10, No. 8 August 1998; 1085-1087 and xe2x80x9cRidge Waveguide Sampled Grating DBR Lasers with 22-nm Quasi-Continuous Tuning Range,xe2x80x9d by B. Mason et al., IEEE Photonics Technology Letters, Vol. 10, No. 9 September 1998, 1211-1213. These widely tunable lasers are based on the use of two multi-element mirrors as described in Coldren U.S. Pat. No. 4,896,325. The former also includes a Y-branch splitter with a detector in each branch for wavelength determination. Disclosures of the foregoing three publications and Coldren U.S. Pat. No. 4,896,325 are incorporated herein by reference.
The present invention provides an optical chip device usable for molecular diagnostics, what I call a tunable laser cavity sensor (TLCS). The TLCS is formed from a reference laser and a sensor laser, each comprising a waveguide having a gain section, a partially transmissive mirror section, and a coherent light beam output section, one or both of the waveguides having a phase control section. The light beam output sections of the reference and sensor lasers are joined to enable the coherent light from these sections to interfere, providing a heterodyned frequency. The sensor laser has a thinned waveguide region exposing evanescent field material to form a cavity and which detects the presence of a molecule by a heterodyned frequency shift.